CN104363042A - GEO-LEO satellite network channel allocation method - Google Patents

Abstract

The embodiment of the invention provides a GEO-LEO satellite network channel allocation method. The method comprises the following steps: receiving a call request from an LEO satellite via a GEO satellite; and judging whether the priority of the LEO satellite is an emergency satellite via the GEO satellite, wherein if so, preferentially allocating a channel to the LEO satellite, and if not, allocating the channel to an LEO satellite with a high priority among LEO satellites communicated with the LEO satellite. According to the method provided by the invention, the problem of low channel resource utilization rate of the existing GEO-LEO satellite network channel allocation in the prior art is solved. As the method is adopted, the utilization rate of satellite system resources is improved, and the real-time transmission of important data is ensured.

Description

GEO-LEO satellite network method for channel allocation

Technical field

The embodiment of the present invention relates to satellite communication field, particularly relates to a kind of GEO-LEO satellite network method for channel allocation.

Background technology

Along with the development of science and technology, satellite communication coverage is more and more wider, does not limit by geographical conditions.In commercial communication, be that other means of communication can not be compared.At present, the application such as satellite television, broadcast, remote monitoring, video conference is more and more extensive.Especially emergency communication aspect, satellite communication have ground communication can not and advantage.Be no matter in city, rural area, mountain area or desert, can satellite communication be realized.LEO satellite has R&D cycle short, the feature such as launch cost is low, propagation delay time is little, obtains and apply more and more widely in meteorology, the hydrology, geological disaster, scientific experimentation etc.Especially in rescue and relief work, because satellite coverage is wide, not by the restriction of ground infrastructure, when the strong natural calamity of generation, other GCF ground communication facilities are destroyed, satellite communication is very necessary a kind of means of communication, in time the condition of a disaster can be conveyed to command centre, be convenient to rescue work and launch.Because LEO satellite orbit is low, shorter with the led to time of ground station, when satellite and ground station not visible time, mass data can only be kept on satellite, poor in timeliness, and a large amount of memory devices makes the load-carrying ability on star weaken.

In order to reduce data transmission delay and the requirement to LEO satellite storage capacity, when LEO satellite and ground station not visible time will forward its data by GEO satellite.But the limited amount of GEO satellite repeater, when many LEO satellites need forwarding data simultaneously, needs GEO satellite channel allocation method reasonable in design.

GEO-LEO satellite network channel allocation of the prior art, has the problem that the utilance of channel resource is low.

Summary of the invention

The embodiment of the present invention provides a kind of GEO-LEO satellite network method for channel allocation, with the problem that the channel resource utilance overcoming GEO-LEO satellite communication of the prior art is too low.

The embodiment of the present invention provides a kind of GEO-LEO satellite network method for channel allocation, comprising:

The call request of GEO satellite reception LEO satellite;

Described GEO satellite judges whether the priority of described LEO satellite is urgent satellite, if so, then preferential by channel allocation give described LEO satellite; If not, then channel allocation is given the LEO satellite of high priority between described LEO satellite and the LEO satellite being in communications status.

Further, after the call request of described GEO satellite reception LEO satellite, also comprise:

GEO satellite according to LEO satellite communication channel quality, LEO satellite remaining can call duration time, fill up time needed for residual memory space and LEO satellite task rank determines that the priority of LEO satellite is urgent satellite or non-emergent satellite.

Further, the priority of described LEO satellite adopts formula

${\mathrm{pir}}_i=\mathrm{lo}{g}_2^{(1+l_i)}\left[\frac{1}{a+\mathrm{\β}+\mathrm{\γ}}(\mathrm{\α}\frac{t_{s\max }-t_{\mathrm{is}}}{t_{s\max }}+\mathrm{\β}\frac{t_{v\max }-t_{\mathrm{iv}}}{t_{v\max }}+\mathrm{\γ}{\mathrm{pir}}_{\mathrm{ti}})\right]---\left(1\right)$

Calculate, wherein, described l _ivalue $l_i=\left\{\begin{array}{cc}1,& {\mathrm{Pe}}_i\≤{\mathrm{Pe}}_y\\ 0,& {\mathrm{Pe}}_i>{\mathrm{Pe}}_y\end{array}\right.,i=\mathrm{1,2},...n;$ Described Pe _ifor LEO _ithe error rate of satellite and GEO satellite communication channel, described Pe _yfor the error rate threshold value that system allows, described t _smaxit is the maximum duration needing to fill up residual memory space in all LEO satellites; Described t _vmaxthat all LEO satellites and the longest of GEO satellite lead to the time; Described t _ivthat the residue of i-th LEO satellite and GEO satellite can lead to the time; Described t _isfor filling up LEO satellite residual memory space required time, described pir _tifor satellite task rank, value is this satellite of 1 expression is urgent satellite, and value is this satellite of 0 expression is non-emergent satellite, described α, β, γ are the weights of three parameters, in order to the request of the urgent satellite of real-time response, require γ>=alpha+beta when weights are arranged, namely urgent satellite priority is the highest.

Further, described, channel allocation is given the LEO satellite of high priority between described LEO satellite and the LEO satellite being in communications status, comprising:

GEO satellite judges that whether the priority of LEO satellite is higher than the first priority threshold value, if, and the priority of described LEO satellite is when being greater than the second priority threshold value with the difference of the lowest priority of the LEO satellite communicated, described LEO satellite is then allowed to seize channel, if not, then described LEO satellite is not allowed to seize channel.

Further, described LEO satellite is seized probability and is expressed as formula

P _pr＝P(pir _C>δ ₁∩(pir _C-pir _min)>δ ₂) (2)

Wherein, described pir _cthe priority of calling satellite; Described pir _minthe lowest priority of the LEO satellite communicated, described δ ₁be the first priority threshold value, described δ ₂it is the second priority threshold value.

Further, before the call request of GEO satellite reception LEO satellite, also comprise:

LEO satellite judges whether normalization memory space is greater than call threshold, if so, then makes a call to GEO satellite, and if not, described LEO satellite continues image data, and described normalization memory space is the ratio of described LEO satellite current data memory space and memory capacity.

Further, the calling probability of described LEO satellite is expressed as formula

P _c=P (M _c> δ ₃| satellite can lead to) (3)

Wherein, described M _clEO satellite normalization memory space, described δ ₃for call threshold.

The call request of embodiment of the present invention GEO satellite reception LEO satellite, and be its allocated channel according to the priority of LEO satellite, solve the problem that utilance that GEO-LEO satellite network channel allocation of the prior art has channel resource is low, method of the present invention not only increases the utilance of satellite system resource, and ensure that the real-time Transmission of significant data.

Accompanying drawing explanation

In order to be illustrated more clearly in the embodiment of the present invention or technical scheme of the prior art, be briefly described to the accompanying drawing used required in embodiment or description of the prior art below, apparently, accompanying drawing in the following describes is some embodiments of the present invention, for those of ordinary skill in the art, under the prerequisite not paying creative work, other accompanying drawing can also be obtained according to these accompanying drawings.

Fig. 1 is GEO-LEO satellite network method for channel allocation flow chart of the present invention;

Fig. 2 is GEO-LEO satellite network structural representation of the present invention;

Fig. 3 is LEO visibility status schematic diagram in GEO-LEO satellite network of the present invention;

Fig. 4 is another flow chart of GEO-LEO satellite network method for channel allocation of the present invention;

Fig. 5 is another flow chart of GEO-LEO satellite network method for channel allocation of the present invention;

Fig. 6 is that in GEO-LEO satellite network method for channel allocation of the present invention emulation, LEO satellite data adds up amount lost schematic diagram;

Fig. 7 is the effective transmitted data amount schematic diagram of LEO satellite in GEO-LEO satellite network method for channel allocation of the present invention emulation;

Fig. 8 is that GEO-LEO satellite network method for channel allocation of the present invention emulation Satellite channel utilization compares schematic diagram;

Fig. 9 is the Relationship Comparison of LEO satellite and GEO satellite communication channel utilance under the present invention's two kinds of methods.

Embodiment

For making the object of the embodiment of the present invention, technical scheme and advantage clearly, below in conjunction with the accompanying drawing in the embodiment of the present invention, technical scheme in the embodiment of the present invention is clearly and completely described, obviously, described embodiment is the present invention's part embodiment, instead of whole embodiments.Based on the embodiment in the present invention, those of ordinary skill in the art, not making the every other embodiment obtained under creative work prerequisite, belong to the scope of protection of the invention.

Fig. 1 is GEO-LEO satellite network method for channel allocation flow chart of the present invention, and as shown in Figure 1, the method for the present embodiment can comprise:

The call request of step 101, GEO satellite reception LEO satellite;

Step 102, described GEO satellite judge whether the priority of described LEO satellite is urgent satellite, if so, then preferential by channel allocation give described LEO satellite; If not, then channel allocation is given the LEO satellite of high priority between described LEO satellite and the LEO satellite being in communications status.

Further, after the call request of described GEO satellite reception LEO satellite, also comprise:

GEO satellite according to LEO satellite communication channel quality, LEO satellite remaining can call duration time, fill up time needed for residual memory space and LEO satellite task rank determines that the priority of LEO satellite is urgent satellite or non-emergent satellite.

Specifically, in GEO-LEO satellite communication, because LEO satellite orbit is higher, be highly about 1km.Thus LEO satellite exists " blind area " in two GEO satellite coverages, namely exist not by region that GEO satellite covers.Therefore, channel reservation mode cannot be adopted in GEO-LEO satellite communication channel distribution method.In satellite communication, interstellar distance is comparatively far away, loss is comparatively large and be subject to the impacts such as solar radiation, and cause satellite communication channel of poor quality, the error rate is higher.The present invention proposes aggregative weighted channel allocation (Comprehensive Weighted Channel Allocation based on ChannelQuality, hereinafter referred to as the CWCA-CQ) method based on channel quality.

Fig. 2 is GEO-LEO satellite network structural representation of the present invention, in GEO-LEO satellite communication, the data of n LEO satellite are when GEO satellite forwards, in satellite communication when certain channel quality exceedes the channel quality requirement of system permission, this channel is unavailable, otherwise, both occupied limited channel resource, effective data cannot have been received again.The error rate Pe of i-th LEO satellite LEOi and GEO satellite communication channel _irepresent, the error rate threshold value that system allows is set to Pe _y, adopt l _irepresent whether i-th channel can be used, then l _ican be expressed as:

$l_i=\left\{\begin{array}{cc}1,& {\mathrm{Pe}}_i\≤{\mathrm{Pe}}_y\\ 0,& {\mathrm{Pe}}_i>{\mathrm{Pe}}_y\end{array}\right.,i=\mathrm{1,2},...n---\left(1\right)$

In satellite communication, between star there is blocking of the earth in channel, in order to realize communicating between star, should first ensure that inter-satellite is visual.GEO satellite and geo-stationary, and LEO satellite is at a relatively high speed around earth running, therefore, as shown in Figure 3, when LEO satellite transit is in the overlay area of GEO satellite, and after the two antenna alignment, both just can link setup communication.For the ease of analyzing, suppose that LEO satellite enters GEO satellite coverage, the two can communicate, and does not consider antenna angle and direction.Because each LEO satellite orbit is different, also different from the led to time of GEO satellite, if according to the principle of " First Come First Served ", the time short and slower satellite of arriving can be led to because communicating without available channel, and the regularity of satellite communication is stronger, this will cause multiple cycle to complete transfer of data, so that LEO satellite data memory space exceeds memory capacity and overflows, obliterated data.Therefore, if LEO satellite transit is to GEO satellite coverage, the time that distance opens GEO satellite coverage is shorter, and the priority of its channel allocation should be higher, prioritised transmission data.Also namely the remaining call duration time of LEO satellite is longer, and the priority of its channel allocation is higher, prioritised transmission data.

Different from ground base station, on satellite, memory capacity is very limited, when memory data output reaches capacity, real-time Transmission cannot will cause loss of data when returning ground base station again.Therefore, satellite channel will consider the memory data output of LEO satellite in distributing.But each LEO satellite bandwidth is different, and average data picking rate is not identical yet.In order to reasonable distribution, the present invention adopts and fills up LEO satellite residual memory space required time and carry out one of condition of priority balance, i.e. the ratio of present satellites residual memory space size and its image data speed, namely

$t_{\mathrm{is}}=\frac{C_{\mathrm{is}}}{R_i}---\left(2\right)$

Wherein, C _isi-th LEO satellite residual memory space size; R _ii-th LEO satellite data acquisition speed, t _isbe worth less, its priority is higher.

Satellite communication plays great function in dual-use, when burst natural calamity or military situation, command centre in the urgent need to understanding the real time information of disaster area or military sensitizing range, this just require in-orbit or the LEO satellite in this region of covering of temporal emission return this area data in real time.For this reason, the present invention is provided with two satellite task ranks, and the satellite covering key area will carry out an urgent task, and satellite task rank is high, is set to urgent satellite; Other satellite task ranks are identical, are non-emergent satellite.Mathematical relationship is described as:

In GEO-LEO satellite communication, LEO satellite transit is in the led to scope of GEO satellite, and LEO satellite can carry out call request.When this LEO satellite is urgent satellite, be preferably its allocated channel, if there is no available channel, then can seize the existing low priority satellite channel communicated, ensure significant data real-time Transmission; When this LEO satellite is non-emergent satellite, and there is not idle channel in system, now determines whether to seize channel according to calling satellite and the priority of the satellite communicated.

According to above-mentioned analysis, in CWCA-CQ method, LEO satellite priority depends on that satellite communication channel quality, satellite remainingly lead to the time, memory space fills up required time and the several parameter of satellite task rank.In order to easy analysis, adopt Scaling Rules method, in CWCA-CQ method, the priority of i-th LEO satellite can be expressed as:

${\mathrm{pir}}_i=\mathrm{lo}{g}_2^{(1+l_i)}\left[\frac{1}{a+\mathrm{\β}+\mathrm{\γ}}(\mathrm{\α}\frac{t_{s\max }-t_{\mathrm{is}}}{t_{s\max }}+\mathrm{\β}\frac{t_{v\max }-t_{\mathrm{iv}}}{t_{v\max }}+\mathrm{\γ}{\mathrm{pir}}_{\mathrm{ti}})\right]---\left(4\right)$

Wherein, l _ivalue is shown in formula (1); t _smaxit is the maximum duration needing to fill up residual memory space in all LEO satellites; t _vmaxthat all LEO satellites and the longest of GEO satellite lead to the time; t _ivthat the residue of i-th LEO satellite and GEO satellite can lead to the time; α, β, γ are the weights of three parameters, in order to the request of the urgent satellite of real-time response, require γ>=alpha+beta when weights are arranged, and namely urgent satellite priority is the highest.

The call request of embodiment of the present invention GEO satellite reception LEO satellite, and be its allocated channel according to the priority of LEO satellite, this priority according to LEO satellite communication channel quality, LEO satellite remaining can call duration time, fill up time needed for residual memory space and LEO satellite task rank is determined.Solve the problem that utilance that GEO-LEO satellite network channel allocation of the prior art has channel resource is low, method of the present invention not only increases the utilance of satellite system resource, and ensure that the real-time Transmission of significant data.

Fig. 4 is another flow chart of GEO-LEO satellite network method for channel allocation of the present invention, and as shown in Figure 4, the method for the present embodiment, comprising:

Step 101, LEO satellite judge whether normalization memory space is greater than call threshold, if so, then make a call to GEO satellite, if not, described LEO satellite continues image data, and described normalization memory space is the ratio of described LEO satellite current data memory space and memory capacity;

The call request of step 102, GEO satellite reception LEO satellite;

Step 103, described GEO satellite judge whether the priority of described LEO satellite is urgent satellite, if so, then preferential by channel allocation give described LEO satellite; If not, then channel allocation is given the LEO satellite of high priority between described LEO satellite and the LEO satellite being in communications status.

Further, the calling probability of described LEO satellite is expressed as formula

P _c=P (M _c> δ ₃| satellite can lead to) (3)

Wherein, described M _clEO satellite normalization memory space, described δ ₃for call threshold.

Specifically, because GEO satellite coverage is wide, therefore, LEO satellite and GEO satellite can call duration time longer, when LEO satellite data amount is less and when also not leaving GEO satellite coverage, its data end of transmission, discharges channel.After completing release channel, satellite will continue image data, and on LEO satellite, memory data output also increases thereupon thereupon, and priority level is converted into the state of emergency, will again to the request of making a call of GEO satellite.LEO satellite judges, just makes a call to GEO satellite, if be not more than, then continue image data when normalization memory space is greater than call threshold.This normalization memory space is the ratio of LEO satellite current data memory space and memory capacity.

The present embodiment, its normalization memory space compares with call threshold by the LEO passing of satelline, just think that GEO satellite makes a call when this normalization memory space is greater than call threshold, solve LEO satellite after completing the data transfer task of self, also continually to the problem that GEO satellite makes a call, avoiding GEO satellite because of LEO makes a call the waste of the system resource caused continually.

Fig. 5 is another flow chart of GEO-LEO satellite network method for channel allocation of the present invention, and as shown in Figure 5, the present embodiment method, comprising:

The call request of step 101, GEO satellite reception LEO satellite;

Step 102, GEO satellite judge that whether the priority of LEO satellite is higher than the first priority threshold value, if, and the priority of described LEO satellite is when being greater than the second priority threshold value with the difference of the lowest priority of the LEO satellite communicated, described LEO satellite is then allowed to seize channel, if not, then described LEO satellite is not allowed to seize channel.

Further, described LEO satellite is seized probability and is expressed as formula

P _pr＝P(pir _C>δ ₁∩(pir _C-pir _min)>δ ₂) (2)

Wherein, described pir _cthe priority of calling satellite; Described pir _minthe lowest priority of the LEO satellite communicated, described δ ₁be the first priority threshold value, described δ ₂it is the second priority threshold value.

Specifically, LEO satellite starts to transmit data after obtaining channel.Memory data output along with transfer of data start decline, priority also decreases.And the LEO satellite not obtaining channel continues image data, its memory data output increases, and priority also increases.If the communication channel quality of two LEO satellites, residue can the same time, that memory space fills up required time is all identical.When the two seizes same channel, will occur that channel frequently switches between.The present embodiment, when the priority of LEO satellite need to meet simultaneously be greater than first threshold be greater than this two conditions of Second Threshold with the priority of this LEO satellite with the difference of the lowest priority of the LEO satellite communicated time, this LEO satellite just can seize the channel communicated.Fig. 6 is GEO-LEO satellite network method for channel allocation program flow diagram of the present invention.

The present embodiment, by limiting further for the priority of LEO satellite, thus avoiding the phenomenon that same channel switches continually between two LEO satellites, improve the operating efficiency of satellite network.

In order to verify the performance of the method for channel allocation that the present invention proposes, compare with FIFO method in emulation.Devise 4 LEO passings of satelline, 1 GEO satellite forwarding data in emulation, the emulation initial setting up of 4 LEO satellites is as shown in table 1.

Table 1 simulated environment is arranged

Wherein, " time period that link error rates meets the demands " refers to that 4 LEO satellites and GEO satellite communication link quality reach the time period of system requirements, in this time period, if LEO satellite distribution has channel, then can send data to GEO.In emulation, assuming that GEO satellite has two transponders, the data of 2 LEO satellites can be forwarded simultaneously.

Fig. 7 shows 4 LEO satellite datas and adds up amount lost.Simulation result shows, only have LEO4 satellite generation low volume data to lose, and in FIFO algorithm except LEO1 satellite, loss of data in various degree all occurs all the other 3 satellites in CWCA algorithm.Loss of data is mainly from two aspects, and one is that LEO satellite channel error code is high, and send data when discontented pedal system error code requires, receiving terminal will be caused correctly cannot to receive data, and mass data is dropped; Two be LEO satellite memory capacity, can to lead to time etc. all limited, according to prerequisite variable principle transmission data, after causing, enter the LEO satellite of GEO coverage without available channel, the data volume of collection constantly increases, after system memory size, there is data from overflow and lose.CWCA algorithm determines satellite priority according to formula (1), and determines whether to seize channel according to constraints, avoids the transfer of data in high bit-error moment, reduces the queuing time of high memory data output satellite.Compared with FIFO method, CWCA method for channel allocation method restrained effectively loss of data, ensure that correctness and the integrality of transfer of data.

Fig. 8 is effective transmitted data amount of each LEO satellite.As seen from the figure, except LEO1 satellite, effective transmitted data amount of CWCA method is apparently higher than FIFO method.In whole transmitting procedure, the error rate of LEO1 satellite channel meets the requirement of system error code all the time, and there is the situation of higher, the discontented pedal system error code requirement of error code in LEO2 ~ LEO4 satellite channel, CWCA method efficiently avoid the transfer of data in high bit-error moment, and FIFO method does not consider channel bit error rate, still data are transmitted when the error rate exceeds System Fault Tolerance scope, cause receiving terminal correctly to receive, valid data transmission quantity reduces greatly.LEO3 satellite is urgent satellite, and only when its channel quality does not reach system requirements, communication disruption, meets the real-time Transmission of urgent satellite data.

Fig. 9 is the Relationship Comparison of LEO satellite and GEO satellite communication channel utilance under two kinds of methods.In figure, FIFO method is still transmitted under the error rate is discontented with pedal system requirement situation simply, has both occupied limited channel resource, and receiving terminal is again less than valid data information, and therefore, channel utilization is far below CWCA method.

Last it is noted that above each embodiment is only in order to illustrate technical scheme of the present invention, be not intended to limit; Although with reference to foregoing embodiments to invention has been detailed description, those of ordinary skill in the art is to be understood that: it still can be modified to the technical scheme described in foregoing embodiments, or carries out equivalent replacement to wherein some or all of technical characteristic; And these amendments or replacement, do not make the essence of appropriate technical solution depart from the scope of various embodiments of the present invention technical scheme.

Claims (7)

1. a GEO-LEO satellite network method for channel allocation, is characterized in that, comprising:

The call request of GEO satellite reception LEO satellite;

Described GEO satellite judges whether the priority of described LEO satellite is urgent satellite, if so, then preferential by channel allocation give described LEO satellite; If not, then channel allocation is given the LEO satellite of high priority between described LEO satellite and the LEO satellite being in communications status.

2. method according to claim 1, is characterized in that, after the call request of described GEO satellite reception LEO satellite, also comprises:

GEO satellite according to LEO satellite communication channel quality, LEO satellite remaining can call duration time, fill up time needed for residual memory space and LEO satellite task rank determines that the priority of LEO satellite is urgent satellite or non-emergent satellite.

3. method according to claim 1 and 2, is characterized in that, the priority of described LEO satellite adopts formula

${\mathrm{pir}}_i={\log }_2^{(1+l_i)}\left[\frac{1}{a+\mathrm{\β}+\mathrm{\γ}}(\mathrm{\α}\frac{t_{s\max }-t_{\mathrm{is}}}{t_{s\max }}+\mathrm{\β}\frac{t_{v\max }-t_{\mathrm{iv}}}{t_{v\max }}+\mathrm{\γ}{\mathrm{pir}}_{\mathrm{ti}})\right]---\left(1\right)$

Calculate, wherein, described l _ivalue $l_i=\left\{\begin{array}{cc}1,& {\mathrm{Pe}}_i\≤{\mathrm{Pe}}_y\\ 0,& {\mathrm{Pe}}_i>{\mathrm{Pe}}_y\end{array}\right.,$ I=1,2 ... n; Described Pe _ifor LEO _ithe error rate of satellite and GEO satellite communication channel, described Pe _yfor the error rate threshold value that system allows, described t _smaxit is the maximum duration needing to fill up residual memory space in all LEO satellites; Described t _vmaxthat all LEO satellites and the longest of GEO satellite lead to the time; Described t _ivthat the residue of i-th LEO satellite and GEO satellite can lead to the time; Described t _isfor filling up LEO satellite residual memory space required time, described pir _tifor satellite task rank, value is this satellite of 1 expression is urgent satellite, and value is this satellite of 0 expression is non-emergent satellite, described α, β, γ are the weights of three parameters, in order to the request of the urgent satellite of real-time response, require γ>=alpha+beta when weights are arranged, namely urgent satellite priority is the highest.

4. method according to claim 1 and 2, is characterized in that, described, channel allocation is given the LEO satellite of high priority between described LEO satellite and the LEO satellite being in communications status, comprising:

GEO satellite judges that whether the priority of LEO satellite is higher than the first priority threshold value, if, and the priority of described LEO satellite is when being greater than the second priority threshold value with the difference of the lowest priority of the LEO satellite communicated, described LEO satellite is then allowed to seize channel, if not, then described LEO satellite is not allowed to seize channel.

5. method according to claim 4, is characterized in that, described LEO satellite is seized probability and is expressed as formula

P _pr＝P(pir _C>δ ₁∩(pir _C-pir _min)>δ ₂) (2)

Wherein, described pir _cthe priority of calling satellite; Described pir _minthe lowest priority of the LEO satellite communicated, described δ ₁be the first priority threshold value, described δ ₂it is the second priority threshold value.

6. method according to claim 1 and 2, is characterized in that, before the call request of GEO satellite reception LEO satellite, also comprises:

LEO satellite judges whether normalization memory space is greater than call threshold, if so, then makes a call to GEO satellite, and if not, described LEO satellite continues image data, and described normalization memory space is the ratio of described LEO satellite current data memory space and memory capacity.

7. method according to claim 6, is characterized in that, the calling probability of described LEO satellite is expressed as formula

P _c=P (M _c> δ ₃| satellite can lead to) (3)

Wherein, described M _clEO satellite normalization memory space, described δ ₃for call threshold.